Phase shift masks are used as one of super-resolution techniques in the photolithography in recent years. As the phase shift masks, various kinds of phase shift masks are proposed. Among them, an auxiliary pattern type phase shift mask is used as a phase shift mask for forming an isolated pattern such as a contact hole.
FIG. 3, (a) is a plan view of an auxiliary pattern type phase shift mask and FIG. 3, (b) is a sectional view taken along dotted line A in FIG. 3, (a). As shown in these figures, the auxiliary pattern type phase shift mask has, on a transparent substrate 20, a main opening 22 formed in a light-shielding film 21 and auxiliary openings 23 provided at the peripheral portion thereof. Further, in order that light passing through the main opening 22 and light passing through each auxiliary opening 23 have a phase difference of about 180 degrees, the auxiliary pattern type phase shift mask has, for example, a substrate etched portion 24 obtained by etching the substrate to a predetermined depth at a portion corresponding to the main opening. It is noted here that the fine line width and forming positions of the auxiliary openings 23 are set such that the light passing through the auxiliary openings 23 is prevented from resolving a resist on a transfer-target substrate.
As a method of manufacturing such an auxiliary pattern type phase shift mask, the following method, for example, is described in Japanese Unexamined Patent Application Publication (JP-A) No. H7-20625 (hereinafter referred to as Patent Document 1).
At first, referring to FIG. 4, description will be made about a conventional auxiliary pattern type phase shift mask manufacturing method (hereinafter referred to as Conventional Method 1) in the invention described in Patent Document 1.
A light-shielding film 21 and a first resist film 25 are formed in order on a transparent substrate 20 (see FIG. 4, (1)).
Then, a pattern corresponding to a main opening and auxiliary openings is exposed by the use of, for example, an electron-beam exposure apparatus and developed to thereby form a first resist pattern 25a. Then, the light-shielding film is etched using the first resist pattern 25a as a mask to thereby form a light-shielding film pattern 21a having a main opening 22 and auxiliary openings 23 (see FIG. 4, (2)). Thereafter, the remaining first resist pattern is stripped (see FIG. 4, (3)).
Then, a second resist film 26 is formed on the surface of the substrate thus obtained (see FIG. 4, (4)).
A pattern corresponding to the main opening is exposed onto the second resist film by the use of, for example, the electron-beam exposure apparatus and developed to thereby form a second resist pattern 26a (FIG. 4, (5)). By etching the substrate using the resist pattern 26a as a mask, a substrate etched portion 24 is formed (FIG. 4, (5)). Thereafter, the remaining second resist pattern 26a is stripped. Thus, an auxiliary pattern type phase shift mask is completed (FIG. 4, (6)).
According to Patent Document 1 as described above, the main opening and the auxiliary openings are so close to each other. Therefore, it is difficult to write both the main opening and the auxiliary openings on the same resist film by electron-beam writing. In order to solve this problem, Patent Document 1 proposes the following method (hereinafter referred to as Conventional Method 2). This method will be described with reference to FIG. 5.
A light-shielding film 21 and a first resist film 27 are formed in order on a transparent substrate 20 (see FIG. 5, (1)).
Then, a pattern corresponding to a main opening is exposed by the use of, for example, an electron-beam exposure apparatus and developed to thereby form a first resist pattern 27a. Then, the light-shielding film is etched using the first resist pattern 27a as a mask to thereby form a light-shielding film pattern 21b having a main opening 22 (see FIG. 5, (2)).
Subsequently, by etching the substrate using the first resist pattern 27a and the light-shielding film pattern 21b as a mask, a substrate etched portion 24 is formed (see FIG. 5, (2)). Thereafter, the remaining first resist pattern 27a is stripped (see FIG. 5, (3)).
Then, a second resist film 28 is formed on the surface of the substrate thus obtained (see FIG. 5, (4)).
A pattern corresponding to auxiliary openings is exposed onto the second resist film 28 by the use of, for example, the electron-beam exposure apparatus and developed to thereby form a second resist pattern 28a. Then the light-shielding film 21 is etched using the second resist pattern as a mask (FIG. 5, (5)). Thereafter, the remaining second resist pattern 28a is stripped. Thus, an auxiliary pattern type phase shift mask is completed (FIG. 5, (6)).